JP2003257098A - Magneto-optical information processor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a miniaturizable magneto-optical information processor in which the edge of a recording mark is accurately detected and circuit constitution for obtaining read signals is made simpler than before. <P>SOLUTION: A light dividing means 21 for dividing reflected light from a recording medium D divides the reflected light into first and second light beams R1 and R2 corresponding to respective bisected areas Bs1 and Bs2 in the track direction Tc of a beam spot Bs and further divides the respective light beams R1 and R2 into first and second polarized light components whose polarization directions are orthogonal. As photodetection means, a first photodetection means 22a for receiving the first polarized light component of the first light R1 and the second polarized light component of the second light R2 and outputting signals corresponding to the total light reception contents and a second photodetection means 22b for receiving the second polarized light component of the first light R1 and the first polarized light component of the second light R2 and outputting the signals corresponding to the total light reception contents are provided. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical information processing device capable of recording and reproducing information by utilizing the magneto-optical effect.

[0002]

2. Description of the Related Art In a magneto-optical disk device, a method of detecting the edge of a recording mark has been widely adopted as a method of increasing the data recording density. On the other hand, in a magneto-optical disk device, a method for obtaining a magneto-optical signal (readout signal) is to irradiate a magneto-optical disk with a light beam so that lights reflected from the magneto-optical disk are orthogonal to each other. There is a method of decomposing into two polarization components and detecting the difference between them. According to such a method, the read signal has a waveform as shown by a broken line d1 in FIG. 5, for example. The level of this signal becomes the minimum when the beam spot is out of the recording mark M, but becomes large when the beam spot reaches the front end Mf or the rear end Mr of the recording mark M, and the central portion of the recording mark M. It becomes the maximum when approaching. Therefore, the front end Mf and the rear end Mr of the recording mark M are
As a method of detecting the above, for example, an average value Th1 of the maximum value and the minimum value of the level of the signal is set as a threshold value, and when the output of the signal reaches the threshold value Th1, the front end Mf or the rear end is reached at that time. A method of determining that a beam spot is formed on Mr is used.

However, in the above method, the edge of the recording mark is detected on the basis of a specific numerical value of the signal level, so that the magneto-optical disk is affected by unevenness of the substrate thickness of the magneto-optical disk. If the amount of reflected light of the recording mark M fluctuates and the value of the signal changes based on the fluctuation, the output level of the signal at that time is the threshold value Th1 even if the beam spot is irradiated to the front end Mf or the rear end Mr of the recording mark M. It will not be. With this, the edge of the recording mark cannot be accurately detected.

Therefore, in the past, for example, there is a magneto-optical disk device disclosed in Japanese Patent Publication No. 7-3710. In this magneto-optical disk device, as shown in FIG. 6, laser light emitted from a semiconductor laser 90 passes through a collimator lens 91, a polarizer 92, a beam splitter 93, and an objective lens 94 to irradiate the magneto-optical disk D. It is configured to be. The light beam applied to the magneto-optical disk D is linearly polarized light. The reflected light from the magneto-optical disk D passes through the objective lens 94 again and then returns to the beam splitter 93.
To the polarization beam splitter 9 through the quarter wavelength plate 95.
It is designed to enter 6. The polarization beam splitter 96 splits the reflected light into an S-polarized component and a P-polarized component. The light of the S-polarized component is received by the two light receiving portions 97a and 97b of the photodetector 97A, and corresponds to the intensity difference of the light received by the light receiving portions 97a and 97b from the comparator (differential amplifier) 98A. The intensity difference signal Sa is output. Similarly, the light of the P-polarized component is detected by the photodetector 97B.
Are received by the two light receiving portions 97c and 97d, and the intensity difference signal Sb corresponding to the intensity difference between the lights is output from the comparator (differential amplifier) 98B. The subtraction circuit (comparator) 99a outputs a read signal Sc corresponding to the difference between the two intensity difference signals Sa and Sb described above, and the read signal processing circuit 99b has the read signal Sc based on this read signal Sc. Determine the contents of data specifically.

Readout signal S obtained by the above method
c is a beam spot Bs formed on the magneto-optical disc D, which is divided into two in the track direction (the direction in which the track extends, which corresponds to the tangential direction of the disc-shaped recording medium. The same applies hereinafter), and This corresponds to a signal based on the difference in the amount of reflected light from the two-divided area. Such a signal has a waveform as shown by the solid line d2 in FIG. 5, and its level becomes minimum or maximum when the beam spots are formed at the front end Mf and the rear end Mr of the recording mark M. According to such a signal, the broken line d in FIG.
Unlike the case where the edge detection is performed based on the signal indicated by 1, the front end Mf of the recording mark M is changed even if the amount of reflected light from the magneto-optical disk fluctuates due to uneven thickness of the substrate of the magneto-optical disk. And, it becomes possible to accurately detect the rear end Mr.

[0006]

In the magneto-optical disk device, it is desired that the circuit structure for producing various signals be as simple as possible and be small in size. However, in the above-mentioned conventional technique, two photodetectors 97A and 97B of two-division type are provided with two comparators 98.
Since a relatively complicated circuit configuration such as connecting A and 98B is adopted, it cannot always be said that the above demand is sufficiently satisfied.

The present invention was devised under such circumstances, and it is possible to accurately detect the edge of a recording mark and to provide a circuit for obtaining a read signal as compared with the conventional one. It is an object of the present invention to provide a magneto-optical information processing device which has a simple structure and can be downsized.

[0008]

DISCLOSURE OF THE INVENTION In order to solve the above problems, the present invention takes the following technical means.

The magneto-optical information processing apparatus provided by the present invention comprises a light irradiating means for irradiating a recording medium with a light beam to form a beam spot, and a light dividing means for dividing the reflected light from the recording medium. A magneto-optical information processing device, comprising: a light detecting means for receiving the light divided by the light dividing means and outputting a signal corresponding to the received light content, wherein the light dividing means comprises: The reflected light is divided into first and second lights corresponding to the respective two divided areas in the track direction of the beam spot, and the first and second lights have first and second polarization directions orthogonal to each other. It is configured to be further divided into a second polarization component, and the light detection means includes a first polarization component of the first light and a second polarization component of the second light.
First light detecting means for receiving the polarized light components of the first light and outputting a signal corresponding to the total received light content, a second polarized light component of the first light and a first polarized light of the second light. Second light detecting means for receiving a component and outputting a signal corresponding to the total received light content of the component.

In a preferred embodiment of the present invention, there is provided a comparator that outputs a signal corresponding to the output difference between the signals output from the first and second photodetecting means.

According to the present invention, the above-mentioned first and second
When the output difference of the signals output from each of the light detecting means is extracted, the signal of this output difference divides the laser spot into two in the track direction, and the amount of reflected light (or reflected light) from the two divided regions. The read signal corresponds to the difference in intensity. According to the present invention, as a means for obtaining such a read signal, the two comparators (differential amplifiers), which are essential in the prior art shown in FIG. 6, are unnecessary. Therefore, as compared with the above-mentioned conventional technique, it is possible to simplify the configuration of the circuit for creating the read signal and reduce the size thereof. Of course, the read signal obtained in the present invention shows a waveform in which the output level becomes maximum or minimum when the beam spot approaches the edge of the recording mark, and is caused by uneven thickness of the substrate of the recording medium. Thus, even if the amount of light reflected from the recording medium fluctuates, a large error can be prevented from occurring in the detection of the front end and the rear end of the recording mark.

In a preferred embodiment of the present invention, the light splitting means includes first and second polarization splitting members capable of splitting the polarization of received light.
Further, the first and second polarization splitting members are provided so as to receive the reflected light by dividing it into halves corresponding to the first and second lights. First and second
A polarization beam splitter or a Wollaston prism can be used as the polarization splitting member.

With such a structure, the reflected light from the recording medium can be split as intended by the present invention with a simple structure.

In another preferred embodiment of the present invention, the first and second polarization splitting members are the first polarization splitting member.
The first polarization component split by the polarization splitting member and the second polarization component split by the second polarization splitting member have the same traveling direction and are split by the first polarization splitting member. The traveling directions of the second polarization component and the first polarization component split by the second polarization splitting member are the same.

According to this structure, the traveling directions of the first polarization component of the first light and the second polarization component of the second light are aligned, and the first polarization component of the first light is aligned. Since the traveling directions of the second polarization component and the first polarization component of the second light are also aligned, they can be easily and appropriately received by the first and second light detection means, respectively. .

Other features and advantages of the present invention will be more apparent from the following description of embodiments of the invention.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, preferred embodiments of the present invention will be specifically described with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. The magneto-optical disk apparatus A of this embodiment includes an optical system 1 for irradiating the magneto-optical disk D with laser light, a read signal detection system 2, a tracking error detection system 3, and a focus error detection system 4. .

The optical system 1 has the same structure as that conventionally known, and after the laser light emitted from the semiconductor laser 10 is collimated by the collimator lens 11,
The objective lens 1 passes through the first beam splitter 12a.
3 is configured to be incident. By focusing the laser light by the objective lens 13, a circular beam spot Bs is formed on the recording layer of the magneto-optical disk D. The light reflected by the magneto-optical disk D passes through the objective lens 13 again, is returned to the first beam splitter 12a, and is reflected thereby to enter the second and third beam splitters 12b and 12c. Is configured. The laser light emitted from the semiconductor laser 10 is linearly polarized light, and the optical system 1 may not be provided with a polarizer. On the recording layer of the magneto-optical disk D, a perpendicularly magnetized film magnetized in a direction perpendicular to the surface of the magneto-optical disk D is formed, and the laser light incident on and reflected by the recording layer is affected by the Kerr effect. The direction of the main shaft rotates.

The read signal detection system 2 creates a read signal (magneto-optical signal) based on the light reflected by the magneto-optical disk D and reflected and separated by the second beam splitter 12b. The half-wave plate 20, the composite beam splitters 21, 2
It has two photodetectors 22 a and 22 b and a differential amplifier 24. The half-wave plate 20 has its crystal axis rotated by 22.5 ° with respect to the incident polarization direction to the magneto-optical disk D, and enhances the sensitivity of rotation detection of the main axis of polarization due to the Kerr effect. To help.

The composite beam splitter 21 is a combination of a pair of polarization beam splitters 21a and 21b. The polarization beams splitters 21a and 21b divide the reflected light that has passed through the half-wave plate 20 into two. It is configured to be incident and incident. More specifically,
As shown in FIG. 2A, the polarization beam splitter 21a
While the first light R1 is incident on the polarization beam splitter 21b, the second light R2 is incident on the polarization beam splitter 21b. The first light R1 is reflected light corresponding to the front half Bs1 (halftone dot pattern portion) when the beam spot Bs is divided into two in the track direction Tc, as shown in FIG. The light R2 is reflected light corresponding to the second half Bs2 (cross-hatched portion). The polarization beam splitter 21a reflects the P-polarized component and transmits the S-polarized component. On the other hand, the polarization beam splitter 21b
On the contrary, it reflects the S-polarized component and transmits the P-polarized component.

In FIG. 1, the photodetector 22a receives the P-polarized component of the first light R1 and the S-polarized component of the second light R2 which are transmitted through the condenser lens 23a and proceed. Therefore, the signal S1 having a level corresponding to the total amount of received light (light intensity) is output. The photodetector 22b is adapted to receive the S-polarized component of the first light R1 and the P-polarized component of the second light R2 that have passed through the condenser lens 23b and proceed, and the total of these components. The signal S2 having a level corresponding to the amount of received light is output. On the light receiving surfaces of the photodetectors 22a and 22b, spots of the S-polarized light component and the spots of the P-polarized light component are formed to overlap with each other, but their polarization directions are different from each other, so that their interference does not occur. , The output levels of the signals S1 and S2 are the same as those when two spots are formed apart from each other. The differential amplifier 24 takes the difference in level between the two signals S1 and S2 output from the photodetectors 22a and 22b, and outputs a read signal S3 obtained by appropriately amplifying the difference.

The tracking error detection system 3 is configured to generate a tracking error signal by, for example, a conventionally known push-pull method, and focuses the light split by the third beam splitter 12c to receive it. It has a condenser lens 30 and a photodetector 31.
The focus error detection system 4 is configured to generate a focus error signal by, for example, converging two semicircular light beams separated by the wedge prism 40 by a condenser lens 42 and then receiving the light by a photodetector 41. ing.

Next, the operation of the magneto-optical disk device A having the above structure will be described.

In this magneto-optical disk device A, the read signal S3 output from the differential amplifier 24 is the sum of the P-polarized component of the first light R1 and the S-polarized component of the second light R2, and the S-polarization component of the first light R1 and P of the second light R2
It corresponds to the difference from the total amount with the polarization component. In other words, the read signal S3 is a signal corresponding to the total value of the difference between the S-polarized components of the first and second lights R1 and R2 and the difference between the P-polarized components of the first and second lights R1 and R2. First half Bs1 and second half Bs2
It corresponds to the difference in the amount of reflected light. Therefore, the characteristic of the read signal S3 is that the read signal Sc output from the conventional subtraction circuit 99a shown in FIG.
The waveform of the read signal S3 when data is read from the magneto-optical disk D is the same as in FIG.
It is similar to the waveform shown in 2. As a result, it becomes possible to accurately detect the front end and the rear end of the recording mark.

In this embodiment, two photodetectors 2 are used.
Only one differential amplifier 24 is used as a means for producing the above-mentioned read signal S3 based on the signals S1 and S2 output from 2a and 22b. Therefore, the configuration of the electric circuit of the read signal detection system 2 can be simplified and the size thereof can be reduced. Two
For the two photodetectors 22a and 22b, it is not necessary to use those whose detection areas are divided into two, and a simple configuration having one detection area may be used, which is also an advantage.

3 and 4 show another embodiment of the present invention. In these figures, the same or similar elements as those in the above embodiment are designated by the same reference numerals as in the above embodiment.

In the magneto-optical disk device Aa of this embodiment, the read signal detection system 2A is provided with the composite Wollaston prism 45, which is different from the above embodiments. This composite Wollaston prism 45
Is the two Wollaston prisms 4 as shown in FIG.
5a and 45b are arranged side by side and combined, and their crystal axes are rotated by 45 ° with respect to the incident polarization direction to the magneto-optical disk D. The mounting with the crystal axis rotated in this manner is similar to the case where the half-wave plate 20 whose crystal axis is rotated by a predetermined angle is provided in the above-described embodiment, and polarization due to the Kerr effect on the surface of the magneto-optical disk D is performed. It helps to improve the detection sensitivity of the rotation of the main shaft.

The Wollaston prisms 45a and 45b are
The light traveling from the second beam splitter 12b is
The first half Bs1 of the beam spot Bs shown in FIG.
1st and 2nd corresponding to the latter half Bs2 respectively
Are arranged side by side so as to be divided into two lights R1 and R2. These Wollaston prisms 45a, 4
5b has a function of separating ordinary light and extraordinary light, which are polarization components orthogonal to each other. However, these two Wollaston prisms 45a and 45b are provided so that the ordinary light and the extraordinary light are deflected in opposite directions, as shown in FIG. As shown in FIG. 4B, as the photodetector 22A, a two-division type having two detection areas 22c and 22d is used.
An ordinary light spot P1a of the first light R1 and an abnormal light spot P2b of the second light R2 are formed in c, and an abnormal light spot P1b of the first light R1 is formed in the detection region 22d. And a spot P2a of the ordinary light of the second light R2 is formed. The spots of ordinary light and extraordinary light overlap with each other as shown in the drawing, but since the polarization directions of these are different, no interference occurs, and the spots of ordinary light and extraordinary light are detected from the photodetector 22A. Signals S1 'and S2' having the same output level as those formed separately are output. The differential amplifier 24 outputs a read signal S3 having a level corresponding to the output difference between the signals S1 'and S2'.

Even with such a configuration, the beam spot Bs is similar to that of the embodiment shown in FIGS. 1 and 2.
It is possible to appropriately obtain the read signal S3 having a level corresponding to the difference in reflected light amount in each of the first half Bs1 and the second half Bs2. Therefore, the same advantages as those of the above embodiment can be obtained.

The present invention is not limited to the contents of the above embodiment. The specific configuration of each part of the optical information processing apparatus according to the present invention can be modified in various ways.

For example, in the configuration shown in FIG. 1, the condenser lenses 23a and 23b are provided between the composite beam splitter 21 and the photodetectors 22a and 22b, respectively. For example, a configuration may be adopted in which one condenser lens is provided in the preceding stage of the composite beam splitter 21. In addition, the first and second aspects of the present invention
The light detecting means may be configured as one photodetector of the two-division type, or may be configured by each of the two photodetectors of the non-division type, and either one may be used. .

The optical information processing apparatus according to the present invention may be constructed by targeting a card-shaped recording medium instead of the disk-shaped recording medium. It goes without saying that, as the light irradiation means, the light splitting means, and the light detection means in the present invention, equipment or parts different from those used in the above-described embodiments can be used.

[0034]

As can be understood from the above description, according to the present invention, the edge of the recording mark can be accurately detected, and the circuit configuration for obtaining the read signal is simpler than the conventional one. It can also be made compact.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the present invention.

FIG. 2A is an explanatory diagram showing a composite beam splitter, and FIG. 2B is an explanatory diagram of a beam spot.

FIG. 3 is an explanatory diagram showing another embodiment of the present invention.

4A is an explanatory diagram showing a composite Wollaston prism, and FIG. 4B is an explanatory diagram of spots formed on a photodetector.

FIG. 5 is a diagram showing a relationship between a position of a beam spot and an output level of a read signal.

FIG. 6 is an explanatory diagram showing an example of a conventional technique.

[Explanation of symbols]

A magneto-optical disk device D magneto-optical disk Bs beam spot 1 Optical system 2 Readout signal detection system 10 Semiconductor laser 13 Objective lens 21 Composite beam splitter 21a, 21b Polarization beam splitter 22A photo detector 22a, 22b photodetector 22c, 22d Detection area 45 Composite Wollaston Prism 45a, 45b Wollaston prism

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 5D075 AA03 CD16 CD19                 5D119 AA01 AA04 AA11 BA01 BB05                       DA05 EC39 JA07 JA25                 5D789 AA01 AA04 AA11 BA01 BB05                       DA05 EC39 JA07 JA25

Claims (5)

[Claims] 1. A light irradiation means for irradiating a recording medium with a light beam to form a beam spot, a light dividing means for dividing reflected light from the recording medium, and a light divided by the light dividing means. And a light detecting means for outputting a signal corresponding to the received light content, wherein the light splitting means outputs the reflected light to the beam spot in the track direction. Of the first and second lights respectively corresponding to the two divided regions in
And the second light, respectively, are further divided into first and second polarization components whose polarization directions are orthogonal to each other, and the light detection means is the first light of the first light. A first component that receives a polarization component and a second polarization component of the second light and outputs a signal corresponding to the total content of the received light components.
And a second light for receiving the second polarized light component of the first light and the first polarized light component of the second light and outputting a signal corresponding to the total received light content thereof. A magneto-optical information processing device, comprising: a detection unit. 2. The magneto-optical information processing apparatus according to claim 1, further comprising a comparator that outputs a signal corresponding to an output difference between the signals output from each of the first and second light detection means. . 3. The light splitting means is configured to include first and second polarization splitting members capable of splitting the polarization of received light, and the first and second polarization splitting members include: The magneto-optical information processing apparatus according to claim 1, wherein the magneto-optical information processing apparatus is provided so that the reflected light is divided into halves corresponding to the first and second lights to be received. 4. The magneto-optical information processing apparatus according to claim 3, wherein each of the first and second polarization splitting members is a polarization beam splitter or a Wollaston prism. 5. The first and second polarization splitting members,
The first polarization component split by the first polarization splitting member and the second polarization component split by the second polarization splitting member
Has the same traveling direction as that of the polarized light component, and the traveling directions of the second polarized light component split by the first polarized light splitting member and the first polarized light component split by the second polarized light splitting member are The magneto-optical information processing device according to claim 3, wherein the magneto-optical information processing device is configured to be the same.